1. Field of the Invention
The present invention relates generally to a rotorcraft transmission system and, more particularly, to a shaft deflection controller for providing equal torque splitting and resonance-free operation to a shaft of the rotorcraft transmission system.
2. Description of Related Art
The prior art has developed a variety of apparatuses and systems for initiating and maintaining shaft alignment. In attempts to achieve accurate shaft alignment during operating conditions, many of these prior art devices implemented flexible shaft-to-shaft connecting devices. Typical shaft-to-shaft connecting devices utilized flexible mountings on high speed shafts. The flexible mountings were either coupled to each other or to the output shafts of the turbine engines. None of these shaft-to-shaft connecting devices, however, operated to provide shaft alignment in the context of a split gearing system.
Conventional flexible disk or diaphragm couplings have also been implemented for achieving shaft alignment, but these couplings were often larger and required more space than was usually available. These conventional couplings also offered little latitude in achieving a specific system stiffness through design implementations. The shaft-to-shaft connecting devices, on the other hand, were designed for those system stiffnesses which resulted in minimal vibration during brief shaft operation at critical vibration speeds. The shafts in these applications were usually operating supercritically, with operating speed values lying above the first critical speeds. The designs functioned to prevent shaft flailing and to retain shaft alignment during operation at critical speeds, as the shafts were brought up to operating speed.
Fundamental differences exist between split torque gearing and shaft-to-shaft connecting devices. The loads involved in a gearing system include radial, axial and tangential forces, in addition to overturning moments. In addition, gear tooth, rim and web deflections must be considered. Conventional torque split gearing designs specifically intended to achieve torque-splitting have typically met with only limited success in achieving equal division of torque. These designs included gear tooth indexing, elastomeric gear web designs and splined mountings requiring exact assembly adjustments for each design. Gear tooth, rim and web dimensions vary from one set to another, even for the same design. The above designs relied on selective adjustments made during assembly to account for these unique dimensions. These methods could not assure torque-splitting in typically-encountered applications, as they must be designed for a limited range of speed and load conditions (known vibration and deflection) and very tight dimensional and assembly tolerances. It is difficult if not impossible, however, to predict the gearing system stiffnesses and tooth deflections during operation, since these change for different load and speed conditions.
Designs of some conventional devices addressed the problem of bearing slippage in some instances, although the retention methods for these designs relied more often on the use of friction to prevent bearing slippage, such as the use of spring clamping. Failsafe features of some of these conventional devices relied upon single stops, such as pins, housing walls, or anti-flail rings, which would make contact abruptly with a flailing shaft. Significant shaft deflection prior to contact with emergency restraints would be unacceptable in a split-torque gearing system, however, since this could result in drive system failures. A need exists in the prior art for an apparatus, which can provide equal torque splitting without relying on selective assembly procedures, operate at sub-critical operation, and prevent deflections from reaching near-critical values before providing restraint.